Standby cathode heating circuit for vacuum tube



G. A. TUMARKIN ETAL Filed Sept. 23, 1965 STANDBY CATHODE HEATING CIRCUITFOR VACUUM TUBE g g i INVENTORS 627,440 A. TUMAAK/A/ 4 MA 76/? N6 BY MATTORNEYs 99 Dunn ll 0x March 12, 1968 United States Patent Office3,373,364 Patented Mar. 12, 1968 ABSTRACT OF THE DISCLOSURE An electriccircuit employing electronic vacuum tubes with heated cathodes isquickly brought to operative condition through the use of a controlswitch by-passed by an inductance which inductance is the relay coil ofa relay of which the contacts control the high voltage supplied to thetubes. When the switch is open, the high voltage to the tubes is cut offby the relay contacts opening and the current to the heaters is reducedbecause of the reactance of the relay coil. The low and high voltagesupplied to the tubes may be through a transformer and the inductancelay-passed switch may be in the primary of the transformer.

This invention relates to a circuit for altering the turn oncharacteristic of an electronic circuit employing heated cathodes and inwhich the current to the heaters of the cathodes is obtained through atransformer.

Electronic equipment or sets such as television and radio sets employingvacuum tubes, particularly with indirectly heated cathode-s, are notinstantaneously responsive to the turning on of the switch to the set,nor to the flow of current through the tube heaters since an appreciabletime must elapse before the cathodes are heated to a state whereinsuflicient electrons are emitted to enable current conduction throughthe vacuum tubes.

It is an object of this invention to create a circuit which willeliminate the delay normally ensuing after the turning on of a controlswitch in a circuit employing heated electron tubes before the circuitis rendered effective.

In a spcific aspect, the invention consists in the use of a relay, thecoil of which is in series with the primary winding of a step-downtransformer and bridges the switch. The contacts of the relay, which arenormally closed, are in series with the mid-tap of a high voltagewinding on the transformer and ground, the high voltage winding beingemployed for supplying high voltage to the tubes. Upon energization ofthe coil, by opening of the switch, the relay contacts are openeddisrupting the high voltage supply in the set.

FIGURE 1 represents a conventional power supply of electronic equipmentutilizing vacuum tubes and some vacuum tubes utilized in the set withheater supply lines thereto.

FIGURE 2 shows a circuit in accordance with this invention.

Referring to the drawings in greater detail, in FIG- URE 1 there isillustrated a power supply of a radio, television or the like. Thispower supply normally utilizes a transformer having a primary 12 of manyturns, a center tapped high voltage secondary 14 of many more turns thanthe primary winding and at least one low voltage winding 16 of muchfewer turns than in the primary winding to supply current to the heatersin the vacuum tubes 17 of the electronic set. Usually a second lowvoltage winding, as winding 18, is employed to provide heating currentfor the cathode in the rectifier tube 20, independently of the heatercurrent supplied by winding 16 to the heaters in the other tubes 17 ofthe set. A switch 22 is in series with a pole of the plug 23 and theprimary of the transformer to control set operation. The lead from therectifier cathode or heater of the rectifier is at high positivepotential (B plus) and the current in that lead is usually filtered by afilter comprised of capacitors 24 and 26 and an inductance 23. Thenegative lead of the high voltage supply is normally grounded to thechassis of the set, as is one side of the low voltage or A supply. Themid tap of the high voltage secondary coil is usually grounded via aline 30. A fuse 32 or equivalent is employed in the transformer primarycircuit to protect the set against excessive current flow therethrough.

The circuit of the invention is shown in FIGURE 2. This circuit differsfrom that shown in FIGURE 1 in the bridging of the switch 22 by the coilwinding 34 of a relay, the armature contacts 36 of the relay being cutinto the line 30. The spring contacts are normally biased to closedposition but are held open when switch 22 is open. When switch 22 isclosed, the relay coil is shorted out, the relay is de-energized and thecontacts close. i

The application of the relay to an existing circuit such as is shown inFIGURE 1 is thus very simple, merely necessitating the bridging of theterminals of switch 22 by the coil winding of the relay and theinterposition of contacts 36 of the relay in the wire 30, or removingwire 30 from ground and attaching it to one contact of the relay andgrounding the other contact.

In use of the circuit of FIGURE 2, when the switch 22 is open, the setis inoperative. At this time the reactance of the inductance inserted inthe circuit, here illustrated as relay coil 34, is in series with thereactance of the primary 12 of the transformer 10 and the voltage acrossthe primary is reduced. Therefore the voltages in the secondaries arereduced proportionally. Also since with the switch 22 open the relaycoil is energized sufficiently to open the relay contacts 36, the groundcircuit to the set has been disrupted and no high voltage or B currentcan flow through the circuit, thus removing B voltage from the anodes,this occurring when the tubes are otherwise not conditioned forcontrolled current conduction therethrough.

When the switch 22 is closed, the reactance of coil 34 is shorted out ofthe circuit and full potential is applied to the primary of thetransformer and therefore normal operating potentials are applied to thevacuum tubes in the set, the contacts 36 being released to their springaction to close and to thereby establish the high voltage or B circuit.

In a practical application of the device the relay coil is in circuitwith the primary of the transformer and is designed to create a 25% dropin the direct line voltage appearing across the primary, producingcorresponding voltage drops in the several secondaries. Under operatingconditions of the set, switch 22 is closed and the voltage developed bywinding 18 is 5 volts. Under inoperative conditions of the set, that isto say with switch 22 open, the voltage developed by winding 18 is about3.75 volts. Similarly while the normal voltage across winding 16 is 6.3volts, with switch 22 open it will be about 4.725 volts.

Having thus described the invention, what is claimed as the inventionis:

1. In an electronic circuit employing at least one vacuum tube having aheater and high voltage electrodes, a circuit means for supplying bothcurrent to said heater and high voltage to said electrodes, a switch insaid circuit means for closing said circuit means, an inductancebridging the switch whereby when the switch is open the reactance of theinductance and the remaining portion of the circuit means maintains thevoltage across the 3 heater at a value ins-ufficient to cause effectiveelectron emission in the tube and when the switch is closed theinductance is short circuited to cause effective electron emissionwithin the tube, and said circuit means including a second switch withopen contacts in the high voltage supply means when the first switch isopen, said inductance being the relay coil of a relay Whose contacts arethe contacts of the second named switch, whereby the high voltage supplymeans to the high voltage electrodes is open when the first switch isopen and closed when the first switch is closed.

2. A circuit as defined in claim 1 in which the high voltage supplymeans includes a transformer having a winding, a terminal of which formsone pole of the high voltage supply, said winding having a tap whichforms a second terminal of the high voltage supply, a line connectingsaid tap to an electrode in said tube, said second switch beingconnected in series in said line.

References Cited UNITED STATES PATENTS 2,872,573 2/1959 Wilson 328-2703,171,084 2/1965 Sziklai 328-270 3,225,302 12/1965 Ojelid 328-270 'DAVIDJ. GALVIN, Primary Examiner.

